Frequency control system



July 26, 1949. 6. R. MILLER 2,477,076

FREQUENCY CQNTROL SYSTEM Filed Oct. 12, 1945 /i/l/1 R 0 VOLTAGE GAS FILLED CURRENT INVENTOR 0. R- MILLER 6P6. esmw A 7'7'ORNE V Patented July 26, 1949 UNITED STATES PATENT OFFICE FREQUENCY CONTROL SYSTEM Ohnier R. Miller, Morristown, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application emu 12, 1945, Serial No. 622,071

11 Claims. 01. 250-36) It is an object of the invention to enable the variation of the frequency of the output of a relaxation oscillator by a variable direct current control signal. 7

It is a further object of the invention to enable the stabilization of the frequency of the output of the relaxation oscillator in a simple and reliable manner. I I

To attain these objects a relaxation oscillator circuit is provided which comprises a preliminary direct current amplifier, an oscillator tube of the gas-filled type and a vacuum tube amplifier. In accordance with one embodiment of the invention, the frequency of the output of the oscillator tube is controlled by varying the cathode potential of the oscillator tube by the application of a variable direct current potential thereto and the frequency of the output of the oscillator tube is stabilized by a feedback circuit comprising a condenser and two diode limiter tubes. The condenser and the diode tubes function to convert the output impulses from the oscillator tube, and

as amplified by the amplifier tube, into surges of current for charging a storage condenser whereby such latter condenser will be charged to a degree commensurate with the frequency of the output from the oscillator tube. The charge in such storage condenser is balanced against a charging current commensurate with the variable direct current potential which controls the oscillator tube whereby any change in the summation of the charges in the storage condenser is effective through the preliminary differential amplifier tube to vary the grid potential of the oscillator tube and to thereby change the period of oscillation until the change in the charge condition is removed.

In accordance with a further embodiment of the invention, the plate and grid potentials of the oscillator tube at which the tube will fire are held to fixed values and the surges of current delivered to the storage condenser by the feedback circuit in accordance with the frequency of the output of the oscillator tube are instru mental in conjunction with the variable control current in creating a potential having a sawtooth wave form at the grid of the oscillator tube, the periodicity of which varies with the potential of the control signal. To insure that the voltage applied to the control condenser asosciated with the oscillator tube shall not exceed a determined value and to prevent the otherwise large negativeswing of the grid voltage from causing a premature and harmful stoppage of the condenser discharge through the oscillator tube, an additional diode limiter tube is provided.

The variation of the control signal voltage may be controlled by a variable resistance device such as a multiterminal switch to the stationary ter-' minals of which diiferent values of potential are applied from a source of direct current through parallelly connected resistances of different values; by a variable voltage divider such as a multiterminal switch, the terminals of which are connected to a plurality of taps of a resistance connected in series with a direct current source; by a potentiometer or by an electronic control.

' While the invention is of quite wide applica-' tion, it is particularly useful in circuits of the type disclosed in the application of R. H. Gumley,:

Serial No. 622,065, filed October 12, 1945 concurrently herewith in which a relaxation oscillator of this type, is employed to simulate in an operational flight trainer the noise incident to thein connection with the accompanying drawing.

inwhich:

Fig. 1 shows one embodiment of the invention; and

1 Fig. 2 shows a further embodiment of the invention.

In each figure of, the drawing, tube V2 is a relaxation oscillator of the gas-filled or thyratron type, Vi is a pentode vacuum tube functioning as a direct current amplifier, tube V3 is an amplifier and tubes V4, V5 and V6 are diode vacuum tubes serving as rectifiers and'limiters. The filaments ofall of these tubes are heated from a source of 6.3 volts alternating current over branches of the bus-bars l and 2. g

In Fig. 1. plate potential is applied from the +-volt bus-bar 3 to the plate of tube Vlf hrough the plate esi tor B1, to the plate of ing resistors R4 and R from which screen grid 5 potential is derived for the amplifier tube VI. Grid bias is supplied-to the grid of tube V2. from the potential-divider including-resistors RI, RB and R1 connected between the +130-volt bus-bar 3 and the l05-volt bus-bar 4 of the direct our.- 10,,

rent supply source and biasing potential is supplied to the grid of amplifier tube V3 through the. grid bias resistor R8. Negative potentialof 80 volts is supplied to the plate of'tlie leit unit' of.

diode tube V4 and negative potential of volts is supplied to the plate of the right unit of diode tube V5 from taps onthevoltage divider" comprising resistors RI I, R|2 and Rl3 connected in series between groundand the -105-volt busbar 4 of the direct current supply source. A variable negative control potentialfor controlling the frequency of the output of the oscillator tube V2 is applied through resistor R9 to the cathode of tube V2 and through resistor R10 to the condenser C6 from the slider of the signal control potentiometer SCP, the winding of which potentiometer is energized over a circuit extending from the -105-volt terminal of the source of direct current, through the calibration rheostat 5, through the winding of such potentiometer and through the calibration rheostat B to ground. The calibration rheostats may be adjusted to determine the upper and lower limits of the potential drop across the winding of potentiometer SCP and thereby the upper and lower limits of the negative potential applicable from the slider of such potentiometer to the cathode of'tube V2 and to the condenser 05. Negative grid biasiissupplied to the grid of amplifier tube V3'through resistor RM.

In Fig. 2, plate potential is applied from the +130-vo1t bus-bar 3 to the plate of tube VI through the plate resistor R2I, to the plate of tube V2 through the plate resistor R22 and choke coil A2l and to the plate of tube V3 through the plate resistor R23, and potential is also applied through resistor R24 to the screen grid of tube VI. From a tap in the voltage divider including resistors R25 and R26'connectedbetweenthe busbar 3 and the negative grounded terminal of the +130-volt plate supply source potential is applied to the cathode of the right unit of diode tube V6. Grid bias is supplied to the grid of tube V2 from the voltage divider comprising resisters R21, R21 and R28 connected between the +130-volt bus-bar 3' and the -l05-volt"bus-bar 4, through the grid'bias resistor R29, grid bias is supplied to the grid of tube V3 from the volt age divider comprising resistors R22, R30 and '4 of the amplifier tube VI from the movable arm of the switch 1 which may be set upon any one of the terminals of the switch, which terminals are connected through resistors of difierent resistance value to conductor 8 which in turn is connected between the 105-volt bus-bar 4 and ground. through the calibration rheostat 9. The moveinentof the'arm ofiswitch 1 will vary the potential applied to the control grid of tube VI.

Alternatively, control potential may be applied to the control grid of tube V! through resistors R31 "and' R38lfrom the movable arm of the switch II which. may be set upon any one of the fixed terminals of the switch to include one or more resistors of the voltage divider comprising resistors R39 to RM, inclusive. The control voltage' may also be-controlled by the electronic device such as the tube V1.

Considering first the manner in which the circuit of Fig. 1 functions; it will be assumed that upon the connection of the +l30-volt source to the bus-bar 3, condenser Ci associated with the oscillator tube V2 becomes charged over a circuit from bus-bar 3, through-resistor R2; c0ndenser Cl and through resistor R15 to ground and as it becomes charged, the potential applied through choke coil-Al to; the plate of tube V2 rises. With the 105-volt source'connected to bus-bar 4, current flows through the potential divider comprising rheostat 5, potentiometer winding SCP and rheostat 6 to ground and-with" the slider of potentiometer SOP assumed to be at the upper terminal of its winding, a minimum value of negative controlsignal potential is derived at the slider and applied through resistor R9 to the cathode of the oscillator tube V2. At this time potential derived at the junction point C of thepotential divider extending from bus-bar 3 through resistors Rig RE' and R1 to bus-bar 4 is applied'to the control grid of tube V2. When now the plate of tube V2 has become sufficientl positive, tube V2 conducts and establishes a low resistance discharge path for condenser Cl, through choke coil Al and over the cathode-plate path through the tube. Condenser Cl now discharges until the potential'across the tube V2 is insufiicientto maintain the cathode to plate-current and the tube stops conducting and'condenser Cl again starts charging.

While the tube V2 is conducting the grid potential of the amplifier tube V3 becomes more negative so that the resistance of tube V3 increases with the result that the charging path from bus-bar 3 through resistor R3 and through condenser 04' to the plate of the right unit of the diode limiter tube V4 becomes effective. With the cathode of this right unit connected to ground theunit becomes'conducting and con- R3l bridged between the +130-volt bus-bar 3 denserC4 now charges therethrough until the and the -10,5-volt bus-bar 4 and negative potential is applied to the plate of the left unit of tube V6 from the voltage divider comprising resistors R32 and R33 connected between the -105-volt bus-bar 4 and ground. Negative'po- 85 voltage divider comprising resistors R34; R35

andR36 connected in series between ground and the -105-volt bus-bar 4; A variable negative control potential for controlling the frequency of the output of the oscillator'tube-V2- maybe potential on the plate of tube V4 becomes zero at which time condenserC4" will cease charging.

Whengthe tube V2ceases to conduct and-condenser Cl' starts to recharge the potential through thecoupling condenser C2 risesandthe grid of amplifier tube V3 becomes more positive with the result that the-resistance of tube V3 decreases. A discharge path for condenser C4 is now efiective from ground through resistor RM, over the cathode-plate path through the tube V3, through condenser (34, over the cathodeplate path through th left unit of tube V4 to the 80volt tapon the potential divider'comprising resistors R! I, RI it and R13. Condenser appliedthrough resistor R31" to the control-grid C4will continue todischargeuntil thepotential applied overthe discharge path through the cathode of the left unit of tube V4 reaches avalue of 80 volts, or the plate potential of'such unit of tube V4. The two units of tube V4 thus function to limit the potential appearing at junction point .A from rising higher than zero or falling lower than -80 volts.

Condenser C4 will now continue to discharge over a path from point A through condenser C5 and over the cathode-plate path through the right unit of tube V5 to the 20-volt tap of the voltage divider from which plate potential is supplied to the plate of the right unit of tube V5. Tube V5 will continue to conduct until, through the charging of condenser C5 from the condenser C4, the potential on the right cathode of tube V5 rises from 80 volts to -20 volts at which time condenser C5 will cease to charge and point B will attain a potential of 20 volts. The right unit of tube V5 thus functions as a limiter to hold the potential of point B from going below 20 volts.

When tube V2 again conducts the grid of amplifier tube V3 becomes more negative and the resistance of tube V3 increases whereupon condenser C4 starts to recharge as previously. described in a path through the right unit of diode tube V4 and the potential at point A now rises to zero. With point B connected to the plate of the left unit-of tube V5 and the cathode of such unit connected to the ungrounded terminal of condenser CB which will at this time be at about 4 volts, the potential on the plate of the left unit of tube V5 will rise until it is positive with respect to the cathode and the left unit of tube V5 will now conduct and establish a low. resistance discharge path from ground through the right unit of tube V4, through condenser C4, through the left unit of tube V5 and to condenser C6 and the charge on condenser C5 will be transferred to condenser C6.

As the condenser C5 discharges the potential on the plate of the left unit of tube V5 decreases. When this potential reaches a value of 4 volts, at which time the potential on both the plate and cathode of the left unit of tube V5 will be 4 volts, the left unit of tube V5 will cease to conduct. When the potential at point A decreases from zero to 80 volts the potential at point. B decreases and as the plate of the left unit of tube V5 now becomes negative to the cathode no current can return from condenser C6 to condenser C5. When the potential at pointB reaches .20 volts, the right unit of tube V5 will now conduct, keeping point B at 20 volts and charging the condenser C5 as the point A decreases to 80 volts. The right unit of tube V5 thus serves to charge condenser C5 whenthe potential at point Bdecreases and the left unit of tube V5 discharges the condenser C5 when the potential at pointB rises. I i

As oscillator tube V2 continues to operate under the control of the cathode control potential and the successive charging and discharging of control condenser CI, the cycle of operations above described is repeated. In response to the repeated charging and discharging of condenser C5 the charge thus applied to condenser C6 will increase andsince the impulses of charge delivered to it bycondenser C5 are allof the same magnitude the charge accumulated by condenser C6 will be a measure of the frequency at which tube V2 is firing. Condenser C6, however, is also charged in the Opposite sense in accordance with the setting of the slider of potentiometer SCP and this to a degree commensurate with the'control signal, by thepotentlal derived at the slider of potentiometer SCP as applied to the condenser through resistor RIB. If -now the potential applied to condenser C6 as a measure of the frequency of the output of oscillator tube V2 is equal to the signal potential, there will be no change in potential at the controlgrid ofthe differential amplifier tube VI and consequently'no change in the potential applied to the control grid of the oscillator tube V2; The oscillator tube will thereforecontinue'tooscillate at the frequency determined by the potential applied to its cathode.

Should the frequency of the output of tube V2 increase beyond that which should be commensurate for the input signal then the charge in condenser CB as a measure of such signal output will increase and become greater than the potential applied to such condenser from the signal input and will result in the grid of tube VI becoming more positive and the potential applied from point C. to the. control grid of'oscillator tube V2 becoming more negative. As a consequence it will become necessary for the condenser CI to charge fora longer interval before the potential applied across the tube will fire the tube. The interval between impulses generated by tube V2 will :then be lengthened and the periodicity *of-the output will be decreased until a balanced condition at the grid of tube :VI is again attained. Conversely, should the frequency of the output of tube V2.:decrease below that which should be commensurate for the .input signal then the charge in condenser. Cfias a measure of such signal output will decrease and become less than the potential applied to suchcondenser from the signal input and will result in the grid of tube VI becoming more negative and the potential applied from point C to the control grid of tube V2 becomingmore positive. As a consequence it will become necessaryfor condenser CI to charge for a shorter interval beforethe potential across the tube will fire the tube. The interval between the impulses generated by tube V2 will thus be shortened and the frequency of the output of tube V2 will be increased until a balanced condition at the grid of tube VI is again attained.

If the "slider. of potentiometer SCP should be moved further toward the lower terminal of its winding thereby increasing the negative potential applied fromsuch slider through resistor R9 to the cathode of tube V2 and through resistor RIB to condenser .05, the cathode to plate current in tube VI will decrease and the grid of tube V2 will become more positive whereby condenser CI will be required to charge to a lower potential before the potential across thetube becomes sufficiently high to cause the tube to fire. The result will be that the'periodicity of the Output tube V2 will increase. 7

The modified circuit disclosed in Fig. 2 is similar to that of Fig. l and functions in much the same manner; To startthe cycle of operations l30 and --volt sources are connected to the bus-bars 3 and 4, respectively and the source of heater current is connected to the bus-bars I and 2 for heating the filaments of all of the tubes. With +-volt potential connected to bus-bar 3 potential is applied through,- resistor R22 to the plate of the right unit of tube VGand with the cathode of such tube supplied with'potential from the potential divider comprising resistors R25 and R26 connected between bus-bar 3 and ground, tube VB functions to. establish a shunt of the cha ging .circuitof condenser C2I so that the char ing potential applledfrom busebsr 3 throu h resistor to condenser Cfl willnot-be hisberthan a desired maximum value. CondensenQZi will: thus become chargeditoa maximum value at a. rate determinedby the timeconstant of the oil: cuit comprising the condenser and resistor R22 and. as it becomes chargcdithepositivepotential applied from bussbar 3 through resistor Rlzrand choke coilR2 I will rise..

It will be assumed that the arm of. switch 1. is connected through condenser dito roundiand through resistor: R31 to the control grid'ofiamplifier tube Vi. so that condenser. C5 becomes charged negatively or discharged-at a rate-determined by the valueof resistor R451'and' the capacitanceof the condenser: As condenserflfidischarges, the potential onthe-gridcftnbeVrl becomes more negative withthe. result that-the potential applied from thepotential dividercoms prising resistors RU, R21 and R28; connected between the bus=bars:3..and 4 become more posi-.

tive until apotential is established across tube,

V2 to cause such tube to conduct. When tube V2 conducts-condenser-C2l then discharges. over a circuit extending, through. such. condenser, through thechoke coil. A2! and over the platecathodepaththrough the tube. When the potential across the tube is insufficient to. maintain the. cathode. to plate current. the. tube stops conductingandcondenser C2! againv starts to recharge;

The interrupted signal generated by the. oscillator tube V2'is applied through thecoupling re-. sistor R30 to the control gridof-theamplifier tube V3 and with positive plate. potential connected to the plate of the latter tube; tub'e V'3 functions to amplify: the interrupted signal outputof tube V2 and to apply the amplified .output'to the work circuit Ill- A portion-of theoutputof-amplifier.

tube V3 is fed back in the iormoiii positive impulses of current to condenser-C6 in the-manner fully described in connection. with the discussion of the circuit of Fig. l.

In the circuit of Fig. 2 the condenser C6: is made of such capacity that each small surge of current therethrough from the left unit of tube V5 will counteractagainst the discharging current applied from switcharm I so-that the potentlal'applied to the gridct amplifier tube Vlwill suddenly become more positive resulting in suddenly causing; the gridpotential of tube V2 to become more negative. As a consequence the potentials applied to the grids of tubes VI and V2 will have saw-toothed wave: forms and tube V2 will become conducting at thepeak of each grid potential wave. a

The potential in the cficondenser will-move between two fixed voltages at any frequencyof the outputimpulses of tube V2,- with the right unit of limiter tube V6 functioning to cause condenser C2! to attain a fixed'potential atthe'time of firing oftube-V2. As the condenser02l has a fixed potential at the instant tube V2 fires-thevoltage on the grid of tube V2 hasa fixed value to cause thetube to fire and which, as above described, is determined by the lowest potential limit of condenser CB-at the instant such condenser receives a surge of current from the tube V5. At the instant tube V2 fires-the square wave at the output of tube. V3 causes ashort surge from condenser C5: to condenserCG -as previousiydescribed... This surgehas a fixed. amplitude and duration at .any frequency: and causes the potential in the GB condenser to rise: aflxed amount. Hence. the. saw-toothed: waver potentials" at the rids c tube V1 d Vlbave the some volta e limitat on for aur re uencyi The dischar e time ithe cond e 5 rom its uonertc its ower limi s is o t o ed by the minal a large value of resistance is included through resistorRAB in'the circuit over the arm of switch i to condenser C6; the time required to discharge condenser C6 tothe same lowerrpotene tial becomes longerv and consequently' the time required: to raise the grid potentialof tube; V2 to-thevalue at. which tube V2 fires will become longer and. tube V2 will fire. at a slower rate. If, conversely, the armof switch l is moved to ter,

minal iii-lover which terminal a-smaller value of:

resistance is included through resistor R4! in thecircuitover-the arm of switch Ito-condenser:

denser CB must be held at'some value above the breakdown value. The only current flow to or from the condenser under' this condition is thegrid current flow of the tube VI. An instant change. of=this control voltage and current condition to a-value forsome desired frequency output will cause. the condenser C6 discharge curveto startfrom the holding voltage value and hence the time to the first output impulse can be controlled by the value of the holding potential and current.

If a peak or saw-toothed wave output is desired, a butler tube may be controlled by the plate circuit of; the V-Zor VI tube. The control circuit for this buffer tube should be designed to impose a fixed impedance load on the V2 or VI tube if it is desired to maintain the above discussedfrequency control.

To limit the-negative potential on the grid of tube V2 to prevent the otherwise negative swing of the grid from causing a, premature and harmful stoppage: of the discharge ofcondenser CH through the tube V2; the grid of tube V2 is connected through resistor R29 with the cathode'of the left unitof tube V6; to the plate of which negative potential is supplied from the potential divider connected from the --volt bus-bar 4 to ground through resistors R32 and R33. When the-potential'on the grid of tube V2 and'thus the.

of tube V6, cathode-plate current .will flow in-the left unit of tube V6 and a portion of the negative potential applied to the grid of'tube V2 thus. exablcd to leakon through the left unit of'tube V Control current for discharging condenser C6 may be-applied fr-om the arm of switch I I through resistor R38, a switch H- serving as a multitap potentiometer for deriving a potential from the resistors-R39 to R44, inclusive, connected in series from conductor 8 to' ground; or a variable control 'currentmay be derived from the; potential divider including resistors R48, R19 and'Rifl connected between the busbars ,3 and 4 endanplied through resistor R51 to condenser-C8 under the control of tube V1, the input circuit of which may be caused to respond to a. variable potential change.

What'is claimed is:

1. In a frequency control system,means includingarelaxation oscillator tube for generating an alternating current wave the frequency of which may be controlled, means for'producing'a first direct current control signal for varying the frequency of said generated output wave, a frequency detector for producing a second direct current signal from said output wave which varies in accordance with the variation in the frequency thereof, and an amplifier tube responsive to the summation of said first and said second direct current signals forapplying a control signal to the input circuit of said oscillator tube to control the output frequency of said tube and to stabilize the effect of the first direct current control signal in varying the output frequency of said oscillator tube.

2. In a frequency control system, means including a relaxation oscillator tube for generatin an alternating current wave the frequency of which may be controlled, means for producing a first direct current control signal, means for applying said signal to the input circuit of said tube for varying the frequency of the generated output wave, a frequency detector for producing a second direct current signal from said output wave which varies in accordance with the variation in the frequency thereof, and a differential amplifier tube responsive to the summation of said first and said second direct current signals for applying a stabilizing signal to the input circuit of said oscillator tube to stabilize the efiect of the first direct current control signal in varying the output frequency of said oscillator tube.

3. In a frequency control system, means including a relaxation oscillator tube for enerating an alternating current wave the frequency of which may be controlled, means for producing a first direct current control signal, means for applying said signal to the input circuit of said tube for varying the frequency of th generated output wave, a frequency detector for producing a second direct current signal from said output wave which varies in accordance with the variation in the frequency thereof, means for storing a derivative of said first direct current signal and said second direct current signal, and an amplifier tube responsive to said storage means for applying a stabilizing signal to the input circuit of said oscillator tube to stabilize the effect of the first direct current control signal in varying the output frequency of said oscillator tube.

4. In a frequency control system, means including a relaxation oscillator tube for generating an alternating current wave the frequency of which may be controlled, means for producing a first direct current control signal, means for applying said signal to the input circuit of said tube for varying the frequency of the generated out ut wave, a frequency detector for producing a second direct current signal from said output wave opposite in polarity to said first direct current signal and which varies in accordance with the variation in the frequency of said output wave, means for storing a derivative of said first direct current signal and said second direct current signal, and an amplifier tube responsive to the unbalance between the signals stored in said storing means for applying a stabilizing signal to the input circuit of said oscillator tube to stabilize the effect of the 10 first direct current signal in varying the output frequency of said oscillator tube.

5. In a frequency control. system, means for generatingan alternating current wave the frequency of which may be controlled,.means comprising a condenser for producing adirect current from said alternating current wave. which varies in accordance with thevariation in the frequency of said alternating current wave, means for causing the charge and discharge .of said condenser in response to alternate half waves of said alternating current wave, means for limiting the magnitude'of each condenser charge, and means for applying the direct current discharge impulses from said condenser to said generating means to control the frequency of said alternating current wave;

6. In a frequency control system, means including a relaxation oscillator tube for generating an alternating current wave the frequency of which may begcontrolled, a limiter tube for limiting the plate potential of said oscillator tube, whereby said plate attains the same potential upon'each conducting cycle of said tube, a, signal control means, and means controlled by said signal control means for generating and applying a potential-having a saw-toothed wave form ofvariable periodicity to the input circuit of said tube, whereby said tube is caused to generate said current-wave at the frequency determined by the periodicity of the wave form of said control potential.

7. In afrequency control system, a gas-filled tube, a condenser connected between the cathode and anode of said tube whereby saidtube functions as a relaxation oscillator to generate an alternating current wave the frequency of which may be controlled, a limiter tube connected in parallel with the charging circuit of said condenser, whereby said condenser attains a fixed voltage level on each charging cycle, a signal control means, and means controlled by said signal control means for generating and applying a potential having a saw-toothed wave form of variable periodicity to the input circuit of said oscillator tube, whereby said tube is caused to generate said current wave at the frequency determined by the periodicity of the Wave form of said control potential.

8. In a frequency control system, means including a relaxation oscillator tube for generating an alternating current wave the frequency of which may be controlled, a signal control means, means controlled by said signal control means for generating and applying a potential having a saw-toothed wave form of variable periodicity to the control grid of said tube, whereby said tube is caused to generate said current wave at the frequency determined by the periodicity of the wave form of said control potential, and means for limiting the negative swing of the grid potential to prevent a premature stoppage of the conduction of said tube.

9. In a frequency control system, means including a relaxation oscillator tube for generating an alternating current wave the frequency of which may be controlled, a condenser, a source of direct current, a signal control means for applying current from said source to said condenser for charging said condenser at variable rates, means for producingdirect current impulses from said alternating current wave which vary in periodicity in accordance with the variation in the frequency of said alternating current wave and for applying said impulses to said condenser gamma of which may ise oontroneo; means for limiting z.

fiiieg'piateoofiefioaicars/aid someone-relay said plate ttaios ms some potestiam on each "conductmums 'oisaid tuber. a: condenser; asdurceiof direuiiremnant; a sigma-E control means .for applying current from said source to said condenser for charging said condenser 27h variable-rates, meams' fior prodnoing'direct currentimpuisesifrom saidi alternaning curnem b wave which vary in periodicity in 'acnordance' with the variation in ihe-v'rreouency :of said; alternating current wave ami-im: appl ymgzsaid impulses 'to said condenser whereby the :potienti-a-l across said condenser is varied in: accordance with a saw-tooiihed wave form. iz'hemeriodioity "of which is'varied by said signai conirolled means, and amplifier tube responsive torthe potential. across said oondenser for applying a control potential having a saw-' tootihedwave fiorm rto the. inputoireiut of said oscillator tube, whereby said. oscillator tube is controlled. so varythe frequency of "the current Wave generatedthereby in accordance with the periodicity of said saw-toothed: condenser potential.

' OHMER R. MILLER.

REFERENCES CITED The following "reieremces-areof record in'the me ofthis rpatetit V UNITED "STATES PATENTS Number OTHER REFERENCES Ber. ENO. 464550,.Be France oa -P. c. pub- 1ishedJ-une8,1943.' 

